This invention relates generally to pipe bending equipment and more particularly concerns machines used to bend steel pipe.
Known pipe bending machines level a pipe against a die with a pin-up located on one side of the die and apply force to the pipe on the other side of the die with a stiff-back, typically powered by hydraulic cylinders, to bend the pipe against the die. The maximum bend typically totals 15-16° and the total is achieved by sequential pulls. In each pull, the pipe is bent approximately ½°. Each pull results in a plastic deformation of the pipe. The cylinders of known machines apply the force directly to the stiff-back. Therefore, known machines generally require large diameter cylinders capable of generating forces in a range of 750,000 pounds. Typically, the cylinders required are in the range of 9-14″ in diameter. Such a requirement imposes serious limitations on capabilities of the machine.
First, the larger the diameter of the cylinder, the greater will be the likelihood of leakage and other defects in cylinder operation. Second, the maximum industry standard cylinder is 8″ in diameter. Therefore, cylinders for this application are currently custom made, usually at two to three times the cost of standard cylinders. Third, even though the custom cylinders are very large, known machines still require the use of tandem cylinders tied together. In this configuration, changes in cylinder orientation occur as the cylinders rotate in slightly different radii. This results in the cylinders competing with each other, reducing the net bending force available. In the worst such cases, the counteracting cylinders may bind. Fourth, the resulting reduced cylinder diameter to stroke ratio can cause the stiff-back to overshoot the intended bending angle of the pipe due to reduced controllability.
It is, therefore, an object of this invention to provide a pipe bending machine that will operate efficiently with standard size cylinders. Another object of this invention is to provide a pipe bending machine in which cylinders are not tied in a possibly competing configuration. It is also an object of this invention to provide a pipe bending machine that reduces the risks of overshooting intended bending angles.